1. Field of the invention
The invention relates to an ink jet recording apparatus that has a recording head that moves across the width of a recording paper and forms images by jetting ink droplets onto the recording paper so as to coincide with printing data. More specifically, the invention is directed to a technique for controlling the quantity of ink in an ink cartridge.
2. Related Art
An ink jet printer is an apparatus (i.e., an ink jet recording apparatus) that includes an ink jet recording head. The ink jet recording head is supplied with ink from a source of ink such as an ink cartridge (i.e., a means for storing ink, which may be referred to as ink storage means for convenience). The ink jet printer also includes means for moving the recording paper relative to the recording head (for convenience, this may be referred to as paper forwarding means. The ink jet printer makes a recording by jetting ink droplets from the recording head in correspondence with a print signal.
Because the ink used is a liquid, an ink jet printer must perform a variety of secondary operations and certain types of processing that are not required in printers having wire dot recording heads or thermal recording heads. In particular, some of the operations required of an ink jet recording apparatus are the charging of ink into the recording head, the forcible sucking and discharging of the ink from the recording head to prevent clogging (due to the volatilization of an ink solvent), and the control over the remaining ink level in the ink storage means.
Particular attention will now be paid to this latter operation, that is, the control over the remaining ink level in an ink storage means such as an ink cartridge.
One approach to controlling over the remaining ink level is a hardware-based detection technique. According to this first approach, liquid level detecting means (such as electrodes) are attached to the ink storage means. This approach has drawbacks. In particular, providing liquid level detection hardware requires a more complicated structure for the ink storage means. This more complicated structure increases the cost of manufacture.
Another approach to controlling the remaining ink level is a software-based approach. This second approach helps to overcome the drawbacks of the first approach. Examples of this second, software-based approach may be found in (1) Examined Japanese Patent Publication No. Hei. 5-19467, (2) Examined Japanese Patent Publication No. Hei. 8-2649, (3) Unexamined Japanese Patent Publication No. Hei. 5-88552, and (4) Unexamined Japanese Patent Publication No. Hei. 7-205419. The foregoing four examples of the second approach mention software which involves steps like:
integrating quantities of ink consumed, using a counter, based on the sum of the product of the number of dots during printing and the quantity of ink to be consumed per ink droplet and the product of the quantity of ink to be sucked per forced sucking operation for preventing the clogging of nozzle openings and the number of sucking operations; PA1 displaying the remaining ink level by storing the integrated quantity of ink consumed; and PA1 allowing the integrated quantity of ink consumed to be reset through an external operation. That is, the approach to the control of the remaining ink level evidenced in the four examples mentioned above is to use software. As the example steps just shown reveal, the general software-based approach takes advantage of the functions of a microcomputer incorporated in the recording apparatus.
An ink jet recording apparatus that controls the remaining ink level by means of software, as in the above-identified second approach, can consecutively compute the quantity of ink consumed in relative terms correctly, although ink end detection accuracy may not be so satisfactory. Therefore, by displaying the thus-computed quantity of ink consumed, the user can be kept informed of how much ink is being consumed. Color ink jet printers now are commonly in practical use. Color ink jet printers use diversified techniques to achieve high printing quality. Some of these diversified techniques include using dark and light inks, adjusting the quantity of ink per ink droplet based on printing data, and changing print resolution in accordance with images and texts. All of these techniques tend to complicate proper control under the second approach described above.
Another complicating factor relates to the maintenance processing of the printer. Maintenance processing includes the actions taken to prevent the clogging of the ink jet recording head. During such maintenance processing, certain quantities of ink are forcibly jetted or flushed from the ink jet recording head. Of course, this ink comes from the ink storage means and must be accounted for. The quantities of ink to be forcibly jetted and flushed are meticulously specified, in a variety of ways, and the actual quantity consumed may vary in accordance with the present or recent operations of the recording head.
The diversified techniques of color ink jet printing and the maintenance processing for preventing clogs result in a very complicated situation for which ink consumption must be predicted under the second (software-based) approach. The above-identified four examples of the second approach for controlling the remaining ink level cannot take care of such a complicated ink consumption situation without producing grave errors. The above-identified software-based approaches do not meet the requirement for providing an accurate determination of the remaining ink level. Because the remaining ink level cannot correctly be computed under the above-identified software-based approaches, there is an increased risk of damage to ink jet recording heads operating under such approaches. In particular, the printer might attempt to jet ink droplets from the ink jet recording head even after all of the ink is used up. Such an operation might easily cause fatal damage to an ink jet recording head due to the ink sucking operations performed for maintenance.
There is yet another drawback to the above-identified four examples of the second approach to control of the remaining ink level. This drawback relates to the already mentioned counter. In particular, there may be a requirement that the user reset the remaining ink level control counter by operating a reset button whenever replacing an ink cartridge. If the user replaces the cartridge without resetting the counter, an inconvenient situation arises. That is, because the user has forgotten to operate the reset button, printing operations cannot be performed even though the ink storage means (i.e., the ink cartridge) has available a plentiful supply of ink.